Conventional reciprocating engines usually operate at a constant compression ratio, i.e. the ratio between the maximum and the minimum volume above the piston. The higher compression ratio, the better efficiency and thereby a lower fuel consumption. However, a too high compression ratio can result in that the engine is subjected to “knocking”. The risk of “knocking” is greater at high engine power, for example high engine load, speed, and acceleration. Consequently, the compression ratio is set as high as possible, but yet as low as to avoid “knocking”.
This implies, that when the engine power is low, i.e. during more normal conditions of operation, the compression ratio could in reality be higher without any risk of “knocking”. Thus, a reciprocating engine having a constant compression ratio does not work at an optimum during all conditions of operation.
For this reason, it is known that, during operation, to change the compression ratio of a reciprocating engine (VCR, Variable Compression Ratio) in dependence of load, speed and acceleration conditions, so that the engine can be more efficiently used.
One way of changing the compression ratio in a reciprocating engine is to support the crankshaft in eccentrics in the cylinder block, whereby by revolving the eccentrics it is possible to control the distance between the crank shaft and the cylinder head, and thus change the combustion volume at the same time as the cylinder stroke is maintained. In a conventional engine, the flywheel, coupling and transmission are usually mounted directly onto the engine. With an eccentrically supported crank shaft, problems can arise when the force is transmitted from the crank shaft to the flywheel, since the position of the crank shaft in the radial direction is not constant over time.
For this reason, different types of couplings have been developed to allow for the force transmission from the crank shaft to flywheel/coupling/transmission.